Current methods for classifying hypertensive patients as having high, normal, or low renin in order to identify correctable forms of secondary hypertension are not useful because of a high incidence of both false positives and false negatives. This protocol evaluates the ability of plasma renin following suppression with saline infusion and stimulation with three 40-mg doses of furosemide to accurately predict those hypertensive patients with correctable forms of hypertension. The role of the adrenergic nervous system, the activity of which is assessed by measurement of plasma norepinephrine, in mediating renin release is also being assessed. These studies are in progress in both normotensive and hypertensive subjects; the data are insufficient to reach any final conclusion.